Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates generally to optical switches and, more particularly, to reflector assemblies and cross-connect switches using such reflector assemblies for direct switching of optical signals between input and output optical fibers.
2. Description of the Background Art
Because of its advantages over conventional electrical transmission mediums, including such advantages as increased bandwidth and improved signal quality, the use of fiber optics in communications networks has become commonplace. However, as with electrical signals transmitted over wires which need to be switched between various wires in order for the signals to reach their intended destinations, optical signals similarly need to be switched between different optical fibers at appropriate junctions so that the optical signals reach their intended destinations.
One method of switching an optical signal between fibers is to convert the optical signal to an electrical signal, employ conventional electronic switching components to switch the electrical signal, and then re-convert the electrical signal to an optical signal. An alternative approach is to employ direct optical switching, wherein the optical signal is directed between fibers. The latter approach has distinct theoretical advantages, including an increase in switching speed and a reduction in signal degradation, because it does note require optical-to-electrical and electrical-to-optical conversions.
When implementing direct optical switching, it is desirable to have the capability to switch an optical signal from any one of a number of optical fibers entering a junction (input fibers) to any one of a number of optical fibers exiting a junction (output fibers). Several ways of achieving this have been previously developed. For example, the use of fixed reflectors in conjunction with bending the fiber ends is a known technique. The fiber ends are not bent to point at one another, but rather are directed at one or more reflectors so that an optical signal from the input fiber is reflected to the output fiber. Another approach is to use moveable reflectors, as described in PCT International Publications Nos. WO 99/66354 xe2x80x9cPlanar Array Optical Switch and Methodxe2x80x9d and WO 99/67666 xe2x80x9cMirror Based Fiber Optic Switch and Control Systemxe2x80x9d, both of which are incorporated by reference herein. As can be expected, it is critical that the optical signal be directed from the input fiber such that it enters the output fiber along an optical pathway that is in substantial alignment with the output fiber. PCT International Publication No. WO 99/66354 describes various approaches to ensuring that the optical signals are properly aligned.
The problem with conventional state of the art optical switches that use moveable reflectors, however, is not the manner in which the reflectors are aligned with the input and output fibers. Techniques for controlling the position of and aligning reflectors in relation to input and output fibers in an optical switch array is well known. The most significant problem with current optical switches is that they rely heavily on microelectromechanical systems (MEMS) technology. Unfortunately, MEMS technology is not yet mature and is quite limited in its capabilities. One-axis mirrors relying on MEMS technology typically employ mechanical hinges which are susceptible to friction and wear. Therefore, such switches in general do not have an indefinite service life. Two-axis mirrors relying on MEMS technology tend to suffer from additional problems arising out of the common use of electrostatic drivers to position the MEMS mirrors. Electrostatic drivers, however, have a very limited linear response range (e.g., tens of microns) which limits the overall size of the mirror and, therefore, the beam size. The smaller the beam size, the shorter a beam can stay collimated after it passes through a collimating lens. This severely limits the path length and, therefore, the total number of fibers (and switching mirrors) that can be employed in an optical cross-connect (OXC) switch. In addition, the associated limited angular range of electrostatic drivers further limits the numbers of mirrors that can be placed in a MEMS optical cross-connect switch.
Because it is desirable to optically couple any input fiber to any output fiber in a cross-connect switch, moveable reflectors that can be positioned over a wide angular range are a necessity. There is also a need to be able to switch large numbers of signals in a limited space and, therefore, a concomitant need for an optical cross-connect switch design that is compact. Accordingly, there is a need for a reflector array design for an optical cross-connect switch which is suitable for mass production of switches, which provides for individually controllable reflectors over a wide angular range, and which does not solely rely on unreliable MEMS technology. The present invention satisfies those needs, as well as others and overcomes the deficiencies in current optical cross connect switching technologies.
The present invention generally comprises reflector assemblies for use in optical cross-connect switches, as well as practical, area efficient, bi-directional, randomly addressable optical cross-connect switches fabricated using such reflector assemblies. More particularly, the invention comprises optical cross-connect switches that employ reflector assemblies with non-MEMS mirrors that can be fabricated using conventional materials and processes. The reflector assemblies are suitable for mass production of reflector assembly arrays (e.g., pallets) for use in optical cross-connect switches that can (i) achieve good telecom reliability and (ii) offer forward extendibility to larger numbers of switchable fibers.
By way of example, and not of limitation, a cross-connect switch fabricated according to the present invention comprises at least two reflector pallets, wherein each reflector pallet comprises a plurality of reflector assemblies configured in an array. Each reflector assembly includes a non-MEMS mirror that can be rotated in relation to a first axis as well as in relation to a second axis that is generally perpendicular to the first axis, and associated means for rotating the mirror. This two-axis system permits a beam to be steered in two-dimensional space, thus allowing any input fiber to be switched to any output fiber. Therefore, to form a cross-connect switch in accordance with the present invention, an array of input optic fibers is positioned in relation to at least a first reflector pallet, and an array of output optic fibers is positioned in relation to at least a second mirror pallet, wherein each reflector assembly is associated with a single optic fiber. As a result of this configuration, the switch is easily scalable for any number of fibers. Furthermore, the reflector assemblies provide for fabrication of a high fiber packing density, small mirror, small coil, low inductance, fast switching and reliable optical cross-connect switch system for mass production.
In an embodiment of a cross-connect switch in accordance with the present invention, reflector pallets are placed on the opposite sides of the fibers, with one pallet directly in the path of the input fibers at preferably an approximately forty-five degree angle in relation to the axis of the input fibers, and the other pallet directly in the path of the output fibers also at preferably an approximately forty-five degree angle in relation to the axis of the output fibers. The distance between the centers of the input/output fiber bundles is approximately the same as that between the centers of the two reflector pallets. In this embodiment, the reflector pallets form a generally planar switch configuration.
In an alternative embodiment of a cross-connect switch in accordance with the preset invention, a plurality of reflector pallets are assembled into an array of pallets or xe2x80x9csuper-palletxe2x80x9d. Each reflector pallet, which serves as an element of the xe2x80x9csuper-palletxe2x80x9d, is arranged with a relative angle of tilt with respect to each other such that the super-pallet is cupped or dome-shaped. As a result, the angular range of operation of each mirror in a mirror module is more balanced about a neutral point. All pallet base planes rest on the xe2x80x9croof topxe2x80x9d of the cross-connect switch, with different planes for each pallet, and associated relative angles between planes. The input and output fibers have corresponding fiber to fiber pitches to match the mirror to mirror pitches, whether on the same or different pallet, to form substantially close to a forty-five degree incident or exit angle on the mirrors.
In an embodiment of a reflector assembly in accordance with the present invention, a mirror module and associated mirror are suspended by a support frame which is in turn suspended by a support base. The components are suspended by flexible wires in a manner that allows the pitch and roll of the mirror module to be controlled. The mirror module includes a coil, as does the support frame. A first pair of opposing electromagnetic control assemblies, each comprising a magnet and a yoke, are positioned in relation to the mirror module, and a second pair of such electromagnetic control assemblies are positioned in relation to the support frame. By selectively energizing the coils, controllable magnetic fields can be generated which create a rotating torque in each of the two rotational axes. By controlling the magnetic fields that are generated, the degree of rotation can in turn be controlled.
In another embodiment of a reflector assembly in accordance with the present invention, the mirror modules employ a unitary mirror mount and support frame (e.g., bobbin) that is suspended by flexible wires from a corresponding support base and which rotates around two axes in relation to the support base. In this embodiment, four coils are attached directly to the mirror mount/support frame to increase structural stiffness and reduce crosstalk between the two rotational axes. In addition, four corresponding magnet assemblies are attached directly to the support base and positioned in relation to the coils. As in the first embodiment, by controlling the magnetic fields that are generated, the degree of rotation can in turn be controlled.
In a still further embodiment of a reflector assembly in accordance with the present invention, the mirror modules are suspended by xe2x80x9cserpentinexe2x80x9d like springs, wherein one end of each spring is attached to or fabricated directly onto a mirror frame and the other end is attached to a mirror or mirror mount. The mirror frame is in turn attached to a support frame. Each mirror or mirror mount is coupled to a plurality of coils of curved or straight shapes via a central stem of hemispherical-shaped flexible material attached to the mirror or mirror mount. In this embodiment, magnets and yokes essentially form a circular magnetic field for the coils. The coils are placed along the circumference of a circle within the mirror, such that when energized by current, a force results along a tangent to the circle.
In another embodiment of a reflector assembly in accordance with the present invention, the driving magnets form all or part of the support frame, and are shaped such that the magnetic pole surfaces become part of a hemisphere around the coils that also substantially form a hemisphere, whether the coils are curved or straight. In this embodiment, only one side of the coil faces the magnet in close proximity, resulting in a lower efficiency than the third embodiment, but with less complexity.
Further embodiments of a reflector assembly and variations of the foregoing embodiments are also included as aspects of the invention.
Beam position sensors, such as photodiodes, can be included on the mirror surface or adjacent to the mirror surface to control the centering of the beam on the mirror surface. Additionally, rotation sensors can be mounted on rotatable portions of the assembly to monitor and control the roll and pitch of the mirror. The rotation sensors could be Hall effect, capacitive, position error sensors (PES) or the like. Alternatively, the rotation sensors could be strain gauges or the like that are mounted on the suspension wires.
An object of the invention is to provide a reflector assembly for an optical cross-connect switch that does not employ MEMS technology.
Another object of the invention is to provide a reflector assembly for an optical cross-connection switch that does not employ electrostatic drivers.
Another object of the invention is to provide a reflector assembly for an optical cross-connect switch that can be fabricated from materials other than silicon.
Another object of the invention is to provide a reflector assembly for an optical cross-connect switch that uses an electromagnetic driving mechanism that includes coils and magnets.
Another object of the invention is to provide a reflector assembly for an optical cross-connect switch that has a larger range of two-dimensional angular motion than in a conventional MEMS switch.
Another object of the invention is to provide a reflector assembly for an optical cross-connect switch that is more reliable than in a conventional MEMS switch.
Another object of the invention is to provide a reflector assembly for an optical cross-connect switch that can be fabricated in the centimeter to sub-centimeter size range.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.